Author:

Bene Poelsema
(MESA+ Institute for Nanotechnology, University of Twente)

Quantum Size Effects (QSE) play an important role in determining the surface
morphology of certain epitaxial metal films on metal and semiconductor
substrates. These give rise to distinct preferred film heights, imposed by a
favourable relationship between the film's Fermi wave length and its
interlayer spacing. QSE in thin films are usually observed on substrates
with a surface projected band gap. We obtained evidence for QSE in Pb and Bi
films deposited on Ni(111) [1].
For Pb on Ni(111) a classic QSE induced stabilization of specific Pb film
thicknesses is obtained in a way very similar to Pb/Si(111). Slow heating of
large QSE-stabilized Pb mesas leads to their ultrafast collapse and
evidences collective motion of giant numbers of Pb atoms, resulting in mass
transport rates much higher than expected form the activation energies
derived from STM observations and DFT calculations for individual processes.
For ultrathin Bi fims on Ni(111), the QSE lead to the evolution of
distinctly different crystalline structures. No longer, a sequence of
preferred heights with one unique crystal structure is observed, but rather
the emergence of different crystalline structures with increasing thickness.
This remarkable observation is attributed to the establishment of specific
favourable relationships between the Fermi wave length and the interlayer
spacing. The film's crystal structure is imposed by QSE, facilitated by the
inclination of Bi towards allotropism.
QSE not only lead to preferred thicknesses of thin layers (2D), as reported
for various systems in the recent past, but can also lead to quantized
nanowire lengths (1D), as we reported for Ir/Ge(001). The preferred
Ir-nanowire lengths correspond to multiples of six unit cells and SPS
measurements support the QSE induced nature of the length quantization.
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[1] T. R. J. Bollmann, R. van Gastel, H. J. W. Zandvliet, and B. Poelsema,
Phys. Rev. Let. 107, 136103 (2011); PRL 107, 176102 (2011). \\[0pt]
[2] T. F. Mocking, P. Bampoulis, N. Oncel, B. Poelsema, Nature Commun. 4,
2387 (2013).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.MAR.G53.4